Effect of Sc Number on Vertical Vortex-induced Vibration of Bridges Based on Precise Damping Adjustment

Under the condition that the aerodynamic shape of the bridge and the incoming wind field are determined, the Sc number is one of the key factors affecting the vortex-induced response of long-span bridges. In order to conduct a refinement study on the effect of Sc number on vertical vortex-induced vibration (VVIV) of long-span bridges, firstly a permanent magnet plate eddy current damper was developed, and it was utilized to provide linear and adjustable viscous damping for the spring-suspended sectional model system. Then wind tunnel test for a section model of a steel-concrete composite girder bridge with wind fairings was conducted under three different wind attack angles of +3°, 0°and -3°, respectively, and several different Sc number. Based on the experiments, the variation of VVIV displacement with the wind velocity for different nominal damping ratio was obtained, the maximum displacement of the VVIV versus Sc number relationship was analyzed by curve fitting, and the higher-order modal vortex-induced vibration response of the bridge was predicted. It is found that the lock-in wind speed region as well as the maximum amplitude decrease with the increase of Sc number under all the three wind attack angles, though their varying tendencies are significantly different. The maximum amplitudes for different Sc numbers can be well predicted by curve fitting of the results of wind tunnel tests for at least three different Sc numbers. On the assumption of the same modal damping ratio, the vortex-induced vibration amplitudes of all vertical bending modes of long-span suspension bridges are almost the same. As a result, the vortex-induced vibration amplitudes of higher-order modes are more difficult to meet the specification limits. The research results provide a novel method for refinement prediction of VVIV response of long-span bridges. © 2022, Editorial Department of Journal of Hunan University. All right reserved.